GBAS (ground-based augmentation systems) are augmentation technologies for improving positioning accuracy of satellite navigation systems within a local range (generally within 150 km) by utilizing differential technologies. The basic principles are as below: a differential correctional is calculated out by means of a ground reference station with known determined location, and then the differential correctional is broadcasted to users, such that onboard users may correct a received satellite positioning signal, thereby improving the positioning accuracy. Accuracy of 1-5 m may be obtained through pseudorange local area differential. If carrier phase local area differential technologies are used, even a centimeter-level result may be obtained. Therefore, in precision approach occasions, GBAS stations may be built to enhance the availability of the satellite navigation systems.
Integrity index is a very important index among four major indexes of satellite navigation. This is because integrity is directly related to safety of the onboard users, and thus it is one of the most concerned indexes for users. At present, integrity performance assessment is based on integrity risk monitoring, a monitoring statistical magnitude is set based on a ground or onboard monitoring station, then monitoring data are compared with a preset threshold, then faults are monitored in time and the corresponding satellite-receiver channels are eliminated in time.
The existing integrity risk monitoring threshold model is based on a lot of integrity monitoring statistical magnitudes. These monitoring statistical magnitudes are specifically classified into two categories: ground side monitoring statistical magnitudes and on-board side monitoring statistical magnitudes. By setting appropriate thresholds for different monitoring statistical magnitudes, cases in which the thresholds are exceeded are characterized as integrity risks. However, with continuous development and improvement of GBAS approach service types, to cover all potential risks as more as possible, more and more monitoring statistical magnitudes appear, and forms of the monitoring magnitudes become more and more complex. If these statistical magnitudes are separately processed based on the existing methods to respectively establish threshold models without regard to the correlation between these statistical magnitudes, two possible problems may be caused, i.e., false dismissal and false alarm. In the former case, other statistical magnitudes are not taken into account when a threshold model of a single monitoring statistical magnitude is established, which causes information insufficiency and the established threshold model too large, leaving out integrity risks needing to consider, and thus causing occurrence of integrity risks. In the latter case, when the integrity risks are calculated, repeated calculation may likely cause the calculated integrity risks too high to reflect actual situations.
Therefore, to solve the above problems and to avoid occurrence of the above situations, it is necessary to derive, based on collected data on the monitoring statistical magnitudes, a method for establishing a threshold model for Beidou ground-based augmentation system integrity risk monitoring.